The invention relates to battery powered electronic devices. In particular, the invention relates to battery fuel gauging for indicating an amount of charge remaining in a battery.
Electronic devices that derive some or all of their operating power from a battery are popular, widely available, and in widespread use. Many of these so-called battery powered electronic devices would be much less marketable without the availability of reliable battery power. In fact, many popular portable electronic devices, such as notebook and laptop computers, hand-held computers and personal digital assistants (PDAs), digital cameras, and cellular telephones, would be of little or no use without a reliable and dependable battery power supply.
Many battery powered electronic devices provide a battery xe2x80x98fuel gaugexe2x80x99 to keep the user informed regarding the reliability of the battery power. A battery fuel gauge is an indicator that shows remaining energy capacity or charge level of the battery. The fuel gauge is intended to keep a user of the device informed of a current or remaining battery charge level and, by extension, a probable remaining operating time of the electronic device. In addition, the fuel gauge, or more precisely, data collected by the electronic device and used to generate the fuel gauge, is often used to determine whether or not a predetermined cut-off point in a discharge profile of the battery has been reached. The cut-off point is a point in the battery discharge profile beyond which adequate power may not be available to insure proper device operation. By detecting if and when the cut-off point has been reached, the device can, among other things, initiate a xe2x80x98soft shut-downxe2x80x99. Such a device initiated soft-shut down can help to prevent or at least mitigate various inopportune or inconvenient consequences of an unexpected loss of adequate operational power at or near an xe2x80x98end of dischargexe2x80x99 of the battery.
While having an accurate battery fuel gauge is useful for and enhances the reliability of battery power supplies for electronic devices, generally implementing such a fuel gauge is not a simple, straightforward task. Simply put, there is no direct means of determining or measuring the current charge level of a battery. Therefore, battery fuel gauging generally employs an indirect approach. Instead of directly measuring charge level, battery fuel gauges generally attempt to predict or infer the charge level from measurements of the dynamic electrical behavior or characteristics of the battery. In most cases, fuel gauging is based on monitoring battery characteristics, such as battery voltage or battery current, as a function of time. The measured data from monitoring one or more of these battery characteristics are then translated into a fuel gauge reading or result using a fuel gauge algorithm.
Unfortunately, the problem of battery fuel gauging is made even more difficult in devices capable of accepting and utilizing batteries of any one of different battery chemistries. In simple terms, a battery is a device that converts chemical energy into electrical energy or electricity. The xe2x80x98chemistryxe2x80x99 of the battery refers to the specific combination of electrolytes and electrode materials used in the battery to create and sustain chemical reactions within the battery that produce electricity. A variety of different battery chemistries are currently commercially available including alkaline, high-energy alkaline, nickel-metal hydride (NiMH), nickel-cadmium (NiCd), and photo lithium or lithiumn-iron sulfide (Lixe2x80x94FeS2). Moreover, all of these chemistries are available in a variety of common battery sizes or form factors, including, but not limited to, an xe2x80x98AAxe2x80x99 size.
The chemistry of a battery is relevant to fuel gauging because of a direct relationship between the chemical reactions and the electrical characteristics of the battery. Essentially all measurable electrical characteristics of a given battery, including but not limited to, open-circuit voltage, loaded voltage, charge capacity, peak current and even re-chargeability are a direct result of the specific chemical reactions taking place within the battery. The unique qualities of a battery""s chemical reaction, such as reaction rate, reaction path, and reactants involved, are sometimes referred to collectively as the xe2x80x98reaction kineticsxe2x80x99 or simply xe2x80x98kineticsxe2x80x99 of the battery. The reaction kinetics of the battery dictate the electrical characteristics of the battery. Thus, any of the electrical characteristics of the battery that might be usefully monitored for fuel gauging will be directly affected by or depend on the battery chemistry.
For example, the open-circuit voltages at full charge, mid charge and end of discharge can and do differ from one chemistry to another. In addition, peak current levels and internal resistance levels differ among the various chemistries, leading to different measured voltages when the batteries are placed under a load. Thus, a fuel gauging approach designed or xe2x80x98calibratedxe2x80x99 for one chemistry may not be particularly accurate or effective for another battery chemistry even in the same form factor.
Despite these problems, most battery powered electronic devices employ one of two methodologies in conjunction with monitoring batteries and providing fuel gauging: current monitoring or voltage slope monitoring. Current monitoring, sometimes called power monitoring, determines the energy capacity remaining in a battery by monitoring the power or current passing into and out of the battery. Current monitoring requires knowledge of the approximate amount of energy that can be drained from the battery before it is fully discharged. As such, the use of power/current monitoring is generally restricted to electronic devices that utilize a battery having known characteristics such as an application-specific battery pack. An application-specific battery pack is typically manufactured and/or distributed under the control of a manufacturer of the electronic device. Therefore, the manufacturer can control the battery pack specifications and thus effectively has some considerable control over the accuracy of the battery monitoring and fuel gauging system. Essentially, the fuel gauge can be calibrated based on a priori knowledge of the application-specific battery pack performance characteristics and chemistry.
Because a priori knowledge of battery characteristics is not available to devices that accept multiple battery chemistries (i.e., devices that do not use an application-specific battery pack), generally the current monitoring approach is not used for fuel gauging in these devices. Instead, these devices generally employ the second methodology, voltage slope monitoring. Voltage slope monitoring monitors a change in battery voltage over a change in time (dv/dt) during battery discharge. The change in voltage with respect to time (dv/dt) is referred to as the voltage slope of the battery. If the voltage slope characteristics are known for a given battery chemistry, a reasonably accurate prediction can generally be made regarding charge level based on a measured voltage at various points during the discharge cycle of the battery. Therefore, a periodic measurement of the battery voltage can be used to monitor the battery and provide battery fuel gauging for the electronic device.
In devices designed to work with any one of multiple battery chemistries, the battery chemistry may not be known a priori. In such multi-chemistry situations, the battery fuel gauge is generally designed to accommodate a lowest common denominator among the potential battery chemistries. In most cases, the fuel gauge is simply calibrated for the battery chemistry most likely to be commonly used in the device. As a result, while the fuel gauge may be relatively accurate for the calibrated battery chemistry, the fuel gauge may be grossly inaccurate for other chemistries. In other words, the accuracy of such a fuel gauge directly depends on the battery chemistry being used at a given moment.
Consider, for example, a fuel gauge in an electronic device using voltage slope monitoring that has been calibrated for alkaline batteries. If lithium-iron disulfide (Lixe2x80x94FeS2, i.e., photo lithium) batteries are used in the device instead of alkaline batteries, the fuel gauge can report the lithium-iron disulfide batteries as having 100% charge up to a point at which the lithium-iron disulfide batteries are approximately 90% discharged. Thus, calibrating for alkaline batteries and using photo lithium batteries can result in a grossly inaccurate fuel gauge reading due to an incorrect assumption with regard to the battery chemistry.
As another example, consider another device having a voltage slope based fuel gauge that is calibrated for NiMH batteries. If, instead of NiMH batteries, alkaline batteries are used, the fuel gauge can report the alkaline batteries as being fully charged until they are approximately 80% discharged. Again, the fuel gauge produces grossly inaccurate results when a battery chemistry other than the calibrated-for chemistry is used in the device. Attempting to design the fuel gauge in a way that spreads the inaccuracy among the various battery chemistries does not generally improve the situation. Typically, this approach merely insures that the fuel gauge is inaccurate for all battery chemistries.
Accordingly, it would be advantageous to have fuel gauging for battery powered electronic devices, wherein the fuel gauging accuracy is not dependant on choosing a battery having any one particular battery chemistry. Such fuel gauging would solve a long-felt need in the area of battery powered electronic devices.
The present invention is a method of adaptive fuel gauging, an adaptive fuel gauge apparatus, and an electronic device having adaptive fuel gauging. The present invention employs battery chemistry identification to improve the accuracy and efficacy of fuel gauging in electronic devices having a battery that accept any one of a plurality of battery chemistries. In addition, the present invention utilizes operational mode information from the electronic device to further improve the fuel gauging. The combination of battery chemistry determination and operational mode fuel gauge adaptation yield more accurate fuel gauging for the electronic device than conventional fuel gauging techniques. Moreover, the present invention can better detect whether the battery has reached a cut-off point, thereby enabling a given battery to be drained to a more optimal discharge voltage level.
In one aspect of the present invention, a method of adaptive fuel gauging in an electronic device having a battery is provided. The device accepts any one of a plurality of different battery chemistries for the battery. The method of fuel gauging comprises determining the battery chemistry of the battery and adapting battery fuel gauging to the determined battery chemistry. In one or more embodiments, the method of fuel gauging further comprises monitoring a characteristic of the battery and generating a fuel gauge reading or result based on the monitored characteristic and the determined battery chemistry. In one or more of the embodiments, the method further comprises determining an operational mode of the electronic device. When the operational mode is determined, the generated fuel gauge reading also is based on the determined mode. Among other things, the generated result can be used to create a fuel gauge display and detect whether or not a cut-off point in the battery discharge profile has been reached.
In another aspect of the present invention, an adaptive fuel gauge apparatus for use in conjunction with an electronic device having a battery is provided. The device accepts any one of a plurality of different battery chemistries for the battery. The fuel gauge apparatus comprises a battery monitor and a controller. The battery monitor monitors a characteristic of the battery and generates measured data. The controller receives the measured data and implements adaptive fuel gauging. The adaptive fuel gauging comprises a fuel gauge reading, a determined chemistry of the battery, and optionally a determined operational mode. The fuel gauge reading is a function of the measured data, the determined battery chemistry and the optionally determined operational mode. Preferably, the controller implements the method of the present invention.
In another aspect of the invention, an electronic device with adaptive fuel gauging is provided. The electronic device has a battery and is capable of using any one of a plurality of different battery chemistries. The electronic device comprises a battery monitor, a controller, a memory, a user interface and a computer program stored in the memory that implements the adaptive fuel gauging. The battery monitor monitors a characteristic of the battery and outputs measured data to the controller. The controller executes the computer program comprising instructions that determine a chemistry of the battery, adapt the fuel gauging to the determined chemistry, and generate a fuel gauge result at the user interface from data for the measured battery characteristic based on the adaptation. In one or more embodiments, the computer program further comprises instructions that determine an operational mode of the device when the data are measured, and further adapt the fuel gauging to the determined operational mode. Preferably, the computer program comprises instructions that implement the method of the present invention. Advantageously in some cases, the adaptive fuel gauging of the present invention can be implemented as a firmware upgrade to an existing electronic device using existing battery monitoring components and other components of the electronic device.
The present invention provides for more accurate battery fuel gauging than conventional approaches in a number of ways. For example, instead of calibrating the fuel gauge for a xe2x80x98lowest common denominatorxe2x80x99 or most common chemistry, the present invention provides adaptive fuel gauging that adjusts or adapts to each specific, determined battery chemistry. By adapting the fuel gauging to the chemistry, fuel gauging is not only more accurate but also accommodates a more precise end of discharge cut-off determination. With a more precise cut-off, a battery""s end-of-life is more readily determinable, thus allowing for various battery chemistries to be drained to a more optimal level. The present invention also can enable feedback to be given to the user on battery type choices that might affect the performance of the electronic device. Additionally, the present invention can be employed to prevent accidental attempts to re-charge batteries having nonrechargeable chemistries.
The accuracy of the battery fuel gauging according to the present invention is further enhanced relative to conventional approaches by utilizing operational mode information for the electronic device. The operational mode, especially a xe2x80x98highxe2x80x99 load operation versus a xe2x80x98low to moderatexe2x80x99 load operation, can significantly affect the monitored characteristics of the battery. The present invention employs operational mode information to adjust the fuel gauging, thereby improving the accuracy of the readings. These and other features and advantages of the invention are detailed below with reference to the following drawings.